right here on "360" after being the first to tell you that fbi investigators have not set foot in the ruins of the american consulate of benghazi, libya. tonight, we're the first it tell you why. the likely reason and from a top law enforcement official. four americans as you know were murdered in the assault, one american ambassador, christopher stevens, that was 2 1/2 weeks ago, 2 1/2 weeks, that saw the administration describe this first as a spontaneous outburst, even though reporting shows that officials knew within 24 hours it was not. today the director of national intelligence, james clapper, explained early evidence supported that theory, so that's why they told the white house and congress. clapper says throughout the investigation, his agency made it clear that the assessment was preliminary and could change. neither his statement nor our source have a time frame. law enforcement officials knew within 24 hours this was a terror attack. reporting reveals that even though the administration says the investigation is going smoothing, the fbi has hit a bump in the road.